1. Field
This invention pertains to granulating metal materials which are capable of reacting with and absorbing hydrogen, and to conditioning or activating the metal material to its state in which it will readily react with and absorb hydrogen.
2. State of the Art
The storage of hydrogen in the form of a granular metal hydride has several advantages over other storage methods such as cryogenic storage of liquid hydrogen or pressurized storage of gaseous hydrogen. Primarily, it is a safe, efficient method of storing hydrogen. The device for storing hydrogen as a metal hydride is commonly referred to as a hydride reservoir, which consists of a pressure vessel or container filled with a granular metal material capable of being converted to a metal hydride. The container is provided with a hydrogen gas connection and a means of handling the thermal load encountered during hydriding (reaction with and absorption of hydrogen) and dehydriding (decomposition of metal hydride and release of hydrogen).
Heretofore, the metal material which was to be utilized in the hydride vessel or container was ground into small particles having a size of about one millimeter or less using conventional reduction equipment capable of handling very hard material. The granular metal material then required conditioning before a practical forward rate of hydriding can be attained. This conditioning involves an activation of the metal material to a state in which it is capable of readily reacting with and absorbing hydrogen. The conditioning involves heating the metal material, subjecting the material to a vacuum to outgas the surface thereof, and flushing the vacuumed material with hydrogen gas which apparently further cleans the particle surfaces of the metal material and initiates a hydriding reaction. However, at the temperature at which the conditioning is accomplished, there is relatively little hydrogen actually absorbed by the metal material. Nevertheless, it is evident from the changes occurring in the metal material that a reaction does occur during the conditioning stage. Severe embrittlement of the metal material occurs, and an appreciable breakdown in particle size takes place (see publication BNL 50589, November 1976 from Brookhaven National Laboratories) during the conditioning stage. Generally, the conditioning stage must be repeated in cyclic fashion to obtain adequate activation, i.e., a second cycle, and usually subsequent cycles, of vacuuming the material and then flushing the material with hydrogen are required following the initial vacuuming and flushing.
3. Objectives
The principal objective of the present invention was to provide a process for simultaneously granulating and conditioning the metal material, whereby the reduction apparatus heretofore necessary in grinding the very hard metal material is eliminated. Another objective was to achieve activation more effectively and more efficiently.